Fluorescent chelating agents are being used to investigate the interactions of substrates and chelating at the zinc ion in the active sites of DNA polymerases, hydroxymethylglutaryl-CoA reductase and alcohol dehydrogenase. The goal of these investigations is to elucidate the catalytic functions of the metal ions in these metalloenzymes. Non-enzymic model reactions for NAD-dependent dehydrogenases are being studied to identify non-covalent interactions capable of enhancing the reactivity of the coenzyme at the active site of these oxidation-reduction enzymes. In addition, the chemical nature of intermediates observed in non-enzymic dihydronicotinamide reductions is being explored. The ligand binding specificity of acetylcholinesterase and the acetylcholine receptorprotein from Torpedo californica is under examination with the use of fluorescent ligands. Rapid kinetic measurements and equilibrium measurements of binding constitute the major avenues of approach.